The hydrofracturing process for stimulating oil/gas well production, also known as “hydrofracing”, entails injecting a viscous hydraulic liquid (known in the industry as a “fracing pad”) into a well to fracture the geologic strata and expose isolated beds of extractable material (usually hydrocarbons, oil, natural gas, etc.).
Following injection of the fracing pad, a water-based slurry of surfactants, acids and solid particles (“proppants”) is added to the well to selectively clean and prop open fractures in the well. Proppants in the slurry remain in an appropriate location after the release of a fracturing pressure. With down well pressures often greater than 5000 pounds per square inch, cleaning and re-fracturing of wells incurring extremely high costs and the extractable materials back-flowing through the remaining proppants, the particulates must exhibit suitable strength, reliability and permeability
Properties desirable in proppants include high strength and a high degree of sphericity to promote flow and dispersion of the proppants within the fracing pad. Other desirable properties include low specific gravity to mitigate settling of the proppants during placement of the fracing pad, as well as consistent failure behavior to accurately predict and promote well permeability.
A variety of materials have been used as proppants. These materials have included ground walnut hulls, Ottawa White Sand, high alumina content kaolin as well as bauxite ores. These materials have been employed in the form of large spherical particles (300 microns-2000 microns) diameter. Other materials that have been considered for use as proppants have included glass and/or glass-ceramic such as mixed glass cullet, metallurgical furnace slags, fly ashes, and mining operation by-products.
Glass spheres are an attractive candidate for use as proppants based on their commercial abundance, ease of manufacture, low cost, and high strength. Candidate materials that meet most of the proppant requirements are spheroidized glass manufactured from industrial byproduct waste streams such as mixed glass cullet, rhyolite, basalt, tholeiite, olivine and/or andesite. Such alternate minerals can include rhyolite, basalt, tholeiite and/or olivine having a nominal composition range in weight percent (wt %) of 49-59 SiO2, 10-20 Al2O3, 0.5-4.5 Fe2O3, 3-13 FeO, 0-10 MgO, 0-16 CaO, 0-7 Na2O, 0-4 K2O, 0-4 TiO2, 0-1 MgO, 0-1 P2O5 plus the presence of trace and/or minor quantities of other transition metal oxides, residual water and/or sulphates.
The utility of spherical glass particles as proppants, however, has been hampered by the tendency of the glass particles to fracture under loading into fine fragments that can “blind” the interstices between individual proppant particles, thereby resulting in decreased permeability and recovery of resources from the well.
A need therefore exists for glass and/or glass ceramic materials such as in the form of spherically shaped particles that overcome these undesirable physical behaviors.